In mobile communication networks, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the mobile communication network is deployed.
In a mobile communications network the motion of the mobile communication terminals (inter alia mobile phones, laptop computers, etc.) in relation to the network nodes (base stations) may cause a Doppler shift, i.e. a frequency offset inter alia of the uplink radio signal (i.e. a signal being transmitted from the mobile communication terminal to the network node) that in turn may degrade the uplink receiver performance. Typically the frequency offset increases as the speed of the relative motion between mobile communication terminal and the network node increases.
In the mobile communications system denoted the Evolved Universal Terrestrial Radio Access (E-UTRA) network there are three uplink channels: the Physical Random Access Channel (PRACH), the Physical Uplink Shared Channel (PUSCH), and the Physical Uplink Control Channel (PUCCH). PRACH has a special mode to deal with high frequency offsets and does not require frequency offset compensation. For PUSCH and PUCCH, on the other hand, frequency offset compensation may be needed in order to mitigate performance degradation at high frequency offsets.
The frequency offset estimation on PUSCH and PUCCH can be based on the phase changes of the received reference signals transmitted together with the data. However, the distribution of the reference signals within PUSCH and PUCCH lead to an ambiguity in the frequency offset estimates due to aliasing.
In E-UTRA the mobile communication terminal, termed User Equipment (UE), connects to the network by first sending a random access preamble on PRACH and then sending a random access message on PUSCH. Since no PUCCH signal has been received before the PUSCH transmission the ambiguity in the frequency offset estimate for PUSCH is not resolved.